1. Field of the Invention
The present invention relates to a signal distortion compensating apparatus and method, and more particularly to a signal distortion compensating apparatus and method in a digital TV translator.
2. Background of the Related Art
A variety of linearizing techniques have been proposed to compensate for non-linear behaviors of radio frequency (RF) high-power amplifiers (HPAs) to allow those RFHPAs to meet a standard associated with digital communication systems. Representative related art linearizing methods include a pre-distortion scheme, a feed-forward scheme, and a look-up table (LUT) scheme using a vector signal analyzer.
First, a linearizing method based on the related art pre-distortion scheme will be described. In accordance with this linearizing method, a pre-distorter is arranged upstream from the main amplifier in an amplifying system. The pre-distorter has characteristics opposite to those of the main amplifier. Thus, the upstream pre-distorter compensates for a signal distortion occurring in a particular direction in terms of gain and phase characteristics when an input signal passes through the main amplifier, thereby maintaining the output signal from the amplifying system to be the same as the input signal in terms of characteristics. The related art pre-distortion linearizing method makes it possible to obtain outputs improved in non-linearity.
In accordance with a linearizing method based on the related art feed-forward scheme, a delay line and an error amplifier are used. When an output signal from a main amplifier amplifying an input signal contains distorted intermodulation components, a 180xc2x0 phase adjustment is conducted for those distorted intermodulation components by the delay line and the error amplifier to offset phase distortions of the intermodulation components. As a result, only the signal components similar to the components of the original input signal are outputted.
However, both of the above described related art pre-distortion and feed-forward linearizing methods can be implemented only with hardware configurations. Further, they are limited and problenmatic in that only the linear distortion can be compensated.
For this reason, a related art linearizing method based on a look-up table scheme using a vector signal analyzer has been mainly used. FIG. 1 is a block diagram schematically illustrating a related art signal distortion compensating apparatus applied to digital TV translators.
Referring to FIG. 1, the related art signal distortion compensating apparatus includes a transmitting unit 100 and a linear/non-linear correction receiving unit 200. The transmitting unit 100 includes a modulator 110 consisting of a vestigial sideband (VSB) processor 111, a linear filter 112, and a non-linear pre-corrector 113. The transmitting unit 100 also includes an intermediate frequency (IF) modulator 120, an up-converter 130, an intermediate power amplifier (IPA) 140, an HPA 150, a directional coupler 160, and an antenna 170. The linear/non-linear correction receiving unit 200 includes a vector signal analyzer 210 consisting of a down-converter 211 and a demodulator 212, and a computer 220.
FIG. 2 is a block diagram schematically illustrating an internal software configuration of the computer 220 for producing a reference signal associated with a distorted signal in the related art signal distortion compensating apparatus shown in FIG. 1. Referring to FIG. 2, the internal software configuration of the computer 220 includes a termination slice unit 221 a linear filter unit 222, a non-linear pre-corrector 223, a root raised cosine (RRC) filter unit 224, a scaling unit 225, a pilot signal recovering unit 228, a complex division unit 226, and a look-up table (LUT) storing memory 227. The related art signal distortion compensating apparatus will now be described in additional detail, in conjunction with FIGS. 1 and 2.
Input data is first applied to the VSB processor 111, which in turn conducts a channel coding for the input signal, thereby producing symbols. The produced symbols are applied to the linear filter 112, which in turn produces an in-phase (I) signal and a quadrature (Q) signal, based on the symbols.
The I and Q signals from the linear filter 112 are transmitted to the IF modulator 120, and then to the up-converter 130. The I and Q signals are subjected to a frequency up-conversion while passing through the up-converter 130. The resultant signals pass through the IPA 140 and HPA 150. The resultant output signal from the HPA 150 is transmitted as a TV signal for general subscribers over the antenna 170 after passing through the directional coupler 160.
However, the TV signal, which is transmitted to general subscribers from the antenna 170, may involve a distortion because the VSB signal outputted from the baseband modulator 110 may be distorted because of non-linear factors of temperature, degradation, and noise while passing through the IF modulator 120, IPA 140, and HPA 150. To correct such a signal distortion, distortion components are extracted from the output signal of the HPA 150 through the directional coupler 160. Based on the extracted distorted signal, a reference signal is also produced in accordance with a termination slice scheme. The reference signal is then compared with the distorted signal. Based on the result of the comparison, the signal distortion of the transmitting unit 100 is measured.
That is, the extracted distorted signal from the directional coupler 160 is applied to the down-converter 211 of the vector signal analyzer 210 that down-converts the up-converted frequency signal into an IF signal of 44 MHz. The resultant signal outputted from the clown-converter 211 passes through the demodulator 212, which in turn extracts I and Q digital data.
Based on the extracted I and Q digital signals from the demodulator 212, a reference signal is produced using the internal software of the computer 220 to correct a distortion in the transmission signal outputted from the transmitting unit. The software producing the reference signal consists of a routine for producing a reference signal for distortion correction based on a distorted signal, which is illustrated in FIG. 2.
Referring to FIG. 2, a source reference signal is produced in the termination slice unit 221 based on the distorted signal. The source reference signal is then sequentially processed by the linear filter unit 222 and the non-linear pre-corrector 223, so that it has the same signal as that of the output from the modulator shown in FIG. 1.
Since the distorted signal has been subjected to a root raised cosine filtering process, a pilot removal process, and a scaling process while passing through the vector signal analyzer, the reference signal should also be subjected to those processes so that it can be compared with the distorted signal. To this end, those processes are implemented in a software fashion by the RRC unit 224 and the scaling unit 225.
The resultant reference signal is then applied to the complex division unit 226 at which the distorted signal emerging from the pilot signal recovering unit 228 is also received. Based on the distorted signal and the reference signal extracted using the distorted signal, the complex division unit 226 produces an LUT coefficient for error calculation and non-lineaarity correction.
The produced LUT coefficient is temporarily stored in the LUT storing memory 227, and then inputted to the linear filter 112 and the non-linear pre-corrector 113 via a standard serial cable such as an RS-232C. The linear distortion may be corrected using an adaptive complex equalizer included in the vector signal analyzer.
As described above, the related art signal distortion compensating apparatus and method applied to digital TV translators have various problems. First, it is necessary to use additional devices such as the vector signal analyzer and computer, which result in a great increase in costs. Second, the signal distortion compensation method based on the look-up table scheme using the vector signal analyzer requires a lengthened period of time for coefficient calculation because it uses software processing. Third, the signal distortion compensation method based on the look-up table scheme using the vector signal analyzer involves a complicated production of the reference signal in that the RF signal outputted after passing through the IF modulator, IPA, and HPA is down-converted again. Fourth, the vector signal analyzer involves an inconvenience in transportation at least in the case when it is to be used for an unmanned translator installed at an alpine region because it is heavy.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
An object of the present invention is to provide an apparatus and method of using same that solves one or more problems caused by the limitations and disadvantages of the related art.
Another object of the present invention is to provide a signal distortion compensating apparatus and method in a digital TV translator that extracts a reference signal from a modulator output of a digital TV translator, and conducts a pre-correction based on the extracted reference signal to compensate for a signal distortion involved in the digital TV translator.
Another object of the present invention is to provide a signal distortion compensating apparatus and method in a digital TV translator that compensates for distorted signals using a software control technique without using additional hardware.
Another object of the present invention is to provide a signal distortion compensating apparatus and method that removes or reduces non-linearity resulting from non-linear devices such as high power amplifiers having non-linear characteristics, or other factors such as degradation or temperature variation.
In order to achieve at least the above-described objects of the present invention in a whole or in parts, there is provided a signal distortion compensating apparatus in a digital TV translator that includes a modulator that modulates an input signal, wherein the modulator outputs baseband signals divided from the input signal, a signal processor that processes the baseband signals from the modulator, and transmits a resultant signal to subscribers, and an auto correction unit that compares the resultant signal outputted by the signal processor in a distorted state with a reference signal derived from the baseband signals of the modulator, and generates a control signal based on the comparison, wherein the modulator receives the control signal and conducts a distortion pre-correction for the input signal.
To further achieve the above-described objects of the present invention in a whole or in parts, there is provided a signal distortion compensating apparatus in a digital TV translator that includes a vestigial sideband (VSB) modulator that modulates an input signal, a signal processor that processes an output signal from the VSB modulator and transmits the processed signal to subscribers, a VSB receiver that receives the processed signal output by the signal processor and generates a VSB demodulation signal based on the processed signal, and a controller that receives the VSB demodulation signal from the VSB receiver, demodulates the VSB demodulation signal, calculates a distortion pre- correction value based on the demodulated signal, and controls the VSB modulator based on the calculated distortion pre-correction value.
To further achieve the above-described objects of the present invention in a xv hole or in parts, there is provided a signal distortion compensating method in a digital TV translator that includes modulating an input signal, dividing baseband signals from the modulated signal, and outputting the divided baseband signals, processing the divided baseband signals to transmit resultant signals to subscribers, and comparing one of the resultant signals, which is distorted during the processing step with an associated one of the divided baseband signals as a reference signal and generating a distortion correction signal, wherein the modulating step further performs pre-distortion correcting responsive to the distortion correction signal.
To further achieve the above-described objects of the present invention in a whole or in parts, there is provided a signal distortion compensating method in a digital TV translator that includes modulating an input signal to output modulated signals, processing the modulated signals and transmitting a resultant signal to subscribers, processing a signal distorted from each of the modulated signals during an execution of the step to extract distortion components from the distorted signal, executing a vestigial sideband demodulation for the distortion components extracted from the distorted signal, and calculating a correction value for the distorted signal based on the demodulated distortion components.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.